Inorganic fertilisers, in particular nitrogen-based fertilisers, have revolutionised agriculture. However effective management of the amount of fertiliser used on land is important for many reasons including economic efficiency and environmental management—excess nitrogen run off from agriculture can enter drinking water causing significant human health concerns, and can also damage fresh water and marine eco-systems. Various techniques are known for monitoring the nitrate level in soil. Typically a soil core is taken, the nitrogen is extracted, and this is then used to predict the amount of nitrogen available to the roots of plants in the soil. However this is a time consuming process typically involving taking a number of soil cores and waiting on average two weeks for the results to come back from the laboratory. Based on the results a farmer will decide, for example, how much nitrate-based fertiliser to use in a spring and/or autumn application.
This procedure is cumbersome, slow and expensive and there is a need for improved techniques, and in particular effective but relatively inexpensive techniques. Such techniques would also be of use in the developing world.
Adamchuk et al (Adamchuk, V., Lund, E., Sethuramasamyraja, B., Morgan, M., Dobermann, A. and Marx, D., 2005. Direct Measurement of Soil Chemical Properties on-the-Go using Ion-Selective Electrodes. Computers and Electronics in Agriculture, vol. 48, no. 3, pp. 272-294) provides a relatively recent review of soil sensing techniques, but all the techniques described there involve extracting a soil sample and analysing it afterwards in an aqueous solution. Ito et al (Ito, S., Baba, K., Asano, Y., Takesako, H., 1996. Development of a Nitrate Ion-Selective Electrode Based on an Urushi Matrix Membrane and its Application to the Direct Measurement of Nitrate Nitrogen in Upland Soils. Talanta, vol. 43, no. 11, pp. 1869-1881) describes a nitrate ion-selective electrode based on Urushi, a natural oriental lacquer. Earlier work by one of the inventors (Miller, A. J. and Zhen R-G., Measurement of intracellular nitrate concentrations in Chara using nitrate-selective microelectrodes, Planta 1991 184:47-52) describes the fabrication of nitrate-selective microelectrodes for measuring nitrate concentrations in plant cells.
There is a need for improvements in measuring/monitoring the levels of nitrate (and other plant nutrients).